Method recvServerFirstMessage

pgconn/auth_scram.go:244–304

(serverFirstMessage []byte)

}

func (sc *scramClient) recvServerFirstMessage(serverFirstMessage []byte) error {
	sc.serverFirstMessage = serverFirstMessage
	buf := serverFirstMessage
	if !bytes.HasPrefix(buf, []byte("r=")) {
		return errors.New("invalid SCRAM server-first-message received from server: did not include r=")
	}
	buf = buf[2:]

	idx := bytes.IndexByte(buf, ',')
	if idx == -1 {
		return errors.New("invalid SCRAM server-first-message received from server: did not include s=")
	}
	sc.clientAndServerNonce = buf[:idx]
	buf = buf[idx+1:]

	if !bytes.HasPrefix(buf, []byte("s=")) {
		return errors.New("invalid SCRAM server-first-message received from server: did not include s=")
	}
	buf = buf[2:]

	idx = bytes.IndexByte(buf, ',')
	if idx == -1 {
		return errors.New("invalid SCRAM server-first-message received from server: did not include i=")
	}
	saltStr := buf[:idx]
	buf = buf[idx+1:]

	if !bytes.HasPrefix(buf, []byte("i=")) {
		return errors.New("invalid SCRAM server-first-message received from server: did not include i=")
	}
	buf = buf[2:]
	iterationsStr := buf

	var err error
	sc.salt, err = base64.StdEncoding.DecodeString(string(saltStr))
	if err != nil {
		return fmt.Errorf("invalid SCRAM salt received from server: %w", err)
	}

	sc.iterations, err = strconv.Atoi(string(iterationsStr))
	if err != nil || sc.iterations <= 0 {
		return fmt.Errorf("invalid SCRAM iteration count received from server: %w", err)
	}
	// Bound server-supplied iteration count to prevent a malicious server from forcing the client
	// to spend unbounded CPU in PBKDF2. PostgreSQL's scram_iterations defaults to 4096; this ceiling
	// is ~2500x that.
	const maxScramIterations = 10_000_000
	if sc.iterations > maxScramIterations {
		return fmt.Errorf("SCRAM iteration count from server too high: %d (max %d)", sc.iterations, maxScramIterations)
	}

	if !bytes.HasPrefix(sc.clientAndServerNonce, sc.clientNonce) {
		return errors.New("invalid SCRAM nonce: did not start with client nonce")
	}

	if len(sc.clientAndServerNonce) <= len(sc.clientNonce) {
		return errors.New("invalid SCRAM nonce: did not include server nonce")
	}